Some of the conventional methods of producing composite particles are the hybrid method, the microcapsule method, the spray coating method and the like, in which particles are coated (covered). For example, in the hybrid method, mother particle and child particle are dryly blended so as to inject (strike) particulates of the child particle into each particulate of mother particle, by means of collision energy (impact force or heat), thereby coating the mother particle with the child particle. The mother particle is made of a polyamide resin, a polyacryl resin, or the like, while the child particle is made of titanium oxide or silica.
However, the hybrid method associated with the dry blending has such a problem that the child particle cannot be injected (struck) into a surface of the mother particle when the mother particle gets harder than a certain level. Thus, the hybrid method is not suitable for producing a composite particle by fixing a particle of inorganic compound, such as titanium oxide, onto a surface of a particle having a bridge structure, such as an amino resin particle.
Besides the method described above, known as a method of processing the amino resin particle into the composite particle is a method in which the particle of the inorganic compound is adhered onto the surface of the amino resin particle by hardening a precursor of the amino resin (an amino resin precursor) in the presence of the inorganic compound. For example, the Publication of Japanese Unexamined Patent Application, Tokukaisho No. 52-51493 (published on Apr. 25, 1977) discloses a method in which a benzoguanamine resin precursor is emulsified with a melamine resin precursor and silica particle, and hardened by means of a catalyst, so as to produce an amino resin composite particle on which the silica particle is adhered.
However, in the method recited in the publication, the amino resin composite particle is obtained by simply hardening the benzoguanamine resin precursor by stirring. This does not fix the particulates of the silica particle on particulates of the amino resin particle. Thus, application of external force onto the amino resin composite particle removes most of the particulates of the silica particle from particulates of the amino resin particle.
In the method recited in the above publication, homomixing is used for the step of emulsification for preparing the amino resin precursor, but it does not concretely suggest the mixing with a shear force application for fixing the inorganic compound on the amino resin particle in steps following the step of emulsification, such as a step of mixing an inorganic compound in and a step of hardening. In short, the above publication suggests only the mixing of the amino resin particle and the inorganic compound. Thus, the above publication does not recite or suggest an amino resin composite particle in which the inorganic compound is fixed on a surface of the amino resin particle., and, of course, does not recite or suggest an amino resin composite particle in which the inorganic compound is fixed, with a high firm-adhering ratio, on a surface of the amino resin particle.
In the above publication, the inorganic compound is adhered on the amino resin particle only for preventing the amino resin particle from being aggregated together in the step of hardening, thus, the inorganic compound will be fallen off when the amino resin particle thus produced by the prior art of the publication is subjected to a usual process of the amino resin particle, such as drying, grinding, separation and classification of particle size, etc. In short, in the particle thus manufactured by the prior art, the inorganic compound is not actually strongly fixed on the surface of the amino resin particle, thereby failing to obtain an amino resin composite particle that attains the later-described object of the present invention.
Therefore, desired is an amino resin composite particle from which less inorganic compound particle is removed even if the external force is applied thereon, that is, an amino resin composite particle in which an inorganic compound particle is firmly adhered (fixed) on a surface of an amino resin composite particle, and a method of producing the amino resin composite particle inexpensively and easily.